The present disclosure relates generally to data transmission in communication systems and, more specifically, to methods and systems for supporting inter-band carrier aggregation with different UL/DL TDD configurations.
As used herein, the terms “user equipment” and “UE” can refer to wireless devices such as mobile telephones, personal digital assistants (PDAs), handheld or laptop computers, and similar devices or other User Agents (“UA”) that have telecommunications capabilities. In some embodiments, a UE may refer to a mobile, wireless device. The term “UE” may also refer to devices that have similar capabilities but that are not generally portable, such as desktop computers, set-top boxes, or network nodes.
In some instances, wireless networks communicate with wireless User Equipment (UE) using, for example, base stations that transmits signals throughout a geographical region known as a cell. For example, long-term evolution (LTE) systems include evolved NodeBs (eNBs) for communicating with UEs. As used herein, the phrase “base station” will refer to any component or network node, such as a traditional base station or an LTE or LTE-A base station (including eNBs), that can provide a UE with access to other components in a telecommunications system. In LTE systems, a base station provides radio access to one or more UEs. The base station comprises a packet scheduler for dynamically scheduling downlink traffic data packet transmissions and allocating uplink traffic data packet transmission resources among all the UEs communicating with the base station. The functions of the scheduler include, among others, dividing the available air interface capacity between UEs, determining the transport channel to be used for each UE's packet data transmissions, and monitoring packet allocation and system load. The scheduler dynamically allocates resources for Physical Downlink Shared CHannel (PDSCH) and Physical Uplink Shared CHannel (PUSCH) data transmissions, and sends scheduling information to the UEs through a control channel.
To facilitate communications, a plurality of different communication channels is established between a base station and a UE including, among other channels, a Physical Downlink Control Channel (PDCCH). As the label implies, the PDCCH is a channel that allows the base station to control a UE during downlink data communications. To this end, the PDCCH is used to transmit scheduling assignment or control data packets referred to as Downlink Control Information (DCI) packets to a UE to indicate scheduling to be used by the UE to receive downlink communication traffic packets on a Physical Downlink Shared Channel (PDSCH) or transmit uplink communication traffic packets on a Physical Uplink Shared Channel (PUSCH) or specific instructions to the UE (e.g., power control commands, an order to perform a random access procedure, or a semi-persistent scheduling activation or deactivation). A separate DCI packet may be transmitted by the base station to a UE for each traffic packet/sub-frame transmission.
It is generally desirable to provide high data rate coverage using signals that have a high Signal to Interference Plus Noise ratio (SINR) for UEs serviced by a base station. Typically, only those UEs that are physically close to a base station can operate with a very high data rate. Also, to provide high data rate coverage over a large geographical area at a satisfactory SINR, a large number of base stations are generally required. As the cost of implementing such a system can be prohibitive, research is being conducted on alternative techniques to provide wide area, high data rate service.
In some cases, carrier aggregation can be used to support wider transmission bandwidths and increase the potential peak data rate for communications between a UE, base station or other network components. In carrier aggregation, multiple component carriers are aggregated and may be allocated in a sub-frame to a UE. Carrier aggregation in a communications network may include component carriers with each carrier having a bandwidth of 20 MegaHertz (MHz) and the total system bandwidth is 100 MHz. In this configuration, a UE may receive or transmit on multiple component carriers (e.g., five carriers), depending on the UE's capabilities. In some cases, depending on the network deployment, carrier aggregation may occur with carriers located in the same band or carriers located in different bands. For example, one carrier may be located at 2 GHz and a second aggregated carrier may be located at 800 MHz.
In network communications, information describing the state of one or more of the carriers or communication channels established between a UE and a base station can be used to assist a base station in efficiently allocating the most effective resources to a UE. Generally, this channel state information (CSI) includes measured CSI at a UE and can be communicated to the base station within uplink control information (UCI). In some cases, in addition to the CSI, UCI may also contain Hybrid Automatic Repeat reQuest (HARQ) acknowledgment/negative acknowledgement (ACK/NACK) information in response to PDSCH transmissions on the downlink. HARQ ACK/NACK transmissions are used to signal successful receipt of data transmissions and to request retransmissions of data that was not received successfully. Depending upon the system implementation, the CSI may include combinations of one or more of the following as channel quality information: Channel Quality Indicator (CQI), Rank Indication (RI), and/or Precoding Matrix Indicator (PMI). For LTE-Advanced (LTE-A) (beginning with Rel-10), depending upon the system implementation, there may be more channel quality information types in addition to the formats listed above.
As for duplex modes, downlink and uplink transmissions are organized into two duplex modes, i.e., frequency division duplex (FDD) mode and time division duplex (TDD) mode. The FDD mode uses paired spectrum where the frequency domain is used to separate the uplink (UL) and downlink (DL) transmission. In TDD systems, on the other hand, unpaired spectrum is used where both UL and DL are transmitted over the same carrier frequency. The UL and DL are separated in the time domain.
In 3GPP LTE TDD systems, a subframe of a radio frame can be a downlink, an uplink or a special subframe (the special subframe comprises downlink and uplink time regions separated by a guard period for downlink to uplink switching). The 3GPP specification defines seven different UL/DL configuration schemes in LTE TDD operations. They are listed in Table 1 as follows:
TABLE 1LTE TDD Uplink-downlink configurationsUplink-Downlink-downlinkto-Uplinkconfig-Switch-pointSubframe numberurationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
In Table 1, D represents downlink subframes, U is for uplink subframes and S represents special frame which include three parts: i) the downlink pilot time slot (DwPTS): ii) the uplink pilot time slot (UpPTS); and iii) the guard period (GP). As Table 1 shows, there are two switching point periodicities specified in the LTE standard, 5 ms and 10 ms. 5 ms switching point periodicity is introduced to support the co-existence between LTE and low chip rate UTRA TDD systems and 10 ms switching point periodicity is for the coexistence between LTE and high chip rate UTRA TDD system. The supported configurations cover a wide range of UL/DL allocations from DL heavy 9:1 ratio to UL heavy 2:3 ratio. Therefore, compared to FDD, TDD systems have more flexibility in terms of the proportion of resources assignable to uplink and downlink communications within a given assignment of spectrum. Specifically, it is possible to distribute the radio resources unevenly between uplink and downlink. This will provide a way to utilize radio resources more efficiently by selecting an appropriate UL/DL configuration based on interference situation and different traffic characteristics in DL and UL.
In regards to scheduling and HARQ timing in LTE TDD, since the UL and DL transmissions are not continuous, the scheduling and HARQ timing relationships are separately defined in the related LTE specifications. Currently, the HARQ ACK/NACK timing relationship for downlink is defined by 3GPP LTE Release 10, an example of which is shown in Table 2 below. The data in Table 2 associates an UL sub-frame n, which conveys ACK/NACK, with DL sub-frames n-ki, i=0 to M−1.
TABLE 2Downlink association set index K: {k0, k1, . . . kM−1}UL-DLConfig-Subframe nuration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4,————8, 7,——64, 63——7, 6, 116, 55, 4—————4——12, 8, 7,6, 5, 4,——————1175——13, 12,———————9, 8, 7, 5,4, 11, 66——775——77—
The uplink HARQ ACK/NACK timing linkage defined by LTE Release 10, an example of which is shown in Table 3 below. Table 3 indicates that the PHICH ACK/NACK received in DL sub-frame i is linked with the UL data transmission in UL sub-frame i-k, k. In addition, for UL/DL configuration 0, sub-frames 0 and 5 include IPHICH=1, k=6. This is because there are two ACK/NACKs transmitted in subframes 0 and 5.
TABLE 3k for HARQ ACK/NACKTDD UL/DLsubframe number iConfiguration01234567890747414646266366646656664746
The UL grant, ACK/NACK and transmission, retransmission relationship is listed in Table 4 below. The UE may upon detection of a PDCCH with DCI format 0 or a PHICH transmission in sub-frame n intended for the UE, adjust the corresponding PUSCH transmission in sub-frame n+k, with k given in Table 4.
For TDD UL/DL configuration 0, the LSB of the UL index in the DCI format 0 is set to 1 in sub-frame n or a PHICH is received in sub-frame n=0 or 5 in the resource corresponding to IPHICH=1, or PHICH is received in sub-frame n=1 or 6, the UE shall adjust the corresponding PUSCH transmission in sub-frame n+7. If, for TDD UL/DL configuration 0, both the MSB and LSB of the UL index in the DCI format 0 are set in sub-frame n, the UE shall adjust the corresponding PUSCH transmission in both sub-frames n+k and n+7, with k given in Table 4.
TABLE 4k for PUSCH transmissionTDD UL/DLsubframe number nConfiguration01234567890464616464244344444454677775